Interpretive Summary: Social behavior, including pair bonding and child care giving, is a critical function in social species like humans. The prairie vole serves as an excellent model of pair bonding between mates and paternal child care giving/participation. Brain and hormonal mechanisms involved in these types of social behavior are not fully understood, but they may be related to factors that mediate responses to psychological stress, including the glucocorticoid hormone, corticosterone. We hypothesized that engaging in pair bonding and paternal care is energetically taxing and increase, via corticosterone, appetite for highly energetic foods (e.g., sucrose). We found evidence that in this monogamous species, pair bonding and caring for young are energetically costly, stimulate weight loss, and a preference for calorically dense sweet food. This work supports an important relationship between social behavior, energy metabolism, and food intake.

Technical Abstract:
The direct costs of paternal care are relatively well documented in primates, however little research has explored these effects in monogamous rodents. The present study examines the long-term effects that pairing and parenting have on male prairie voles. We hypothesized that there would be a significant weight loss over the course of pairing and parenting, presumably from the energetic demands that accompany these changes in social condition. In a longitudinal study, we followed ten male prairie voles through being housed with their brother; paired with a female; and caring for three consecutive litters.We found a significant drop in bodyweight across time, with maximum weight loss near the weaning of the first litter. At that same time, feeding increased, leading to possible recovery in weight; however, leptin levels dropped precipitously across time and did not recover. Corticosterone did not change significantly across time points, and overall activity
levels also did not vary significantly over the course of the study. In addition, newly paired males showed a significant increase in preference for a 2% sucrose solution during a three-hour test, indicating a metabolic need for more calories. A cross-sectional study confirmed leptin and corticosterone findings, and showed significant loss of subcutaneous (inguinal) fat in males that had cared for a litter of pups, when compared to males housed with their brothers or newly paired males. These results suggest that cohabitation with a female, and caring for pups, all have costs for male prairie voles.